题目:
Given a singly linked list, determine if it is a palindrome.
代码实现:
/**
* Definition for singly-linked list.
* public class ListNode {
* int val;
* ListNode next;
* ListNode(int x) { val = x; }
* }
*/
public class Solution {
public boolean isPalindrome(ListNode head) {
if (head == null) {
return true;
}
ListNode middle = findMiddle(head);
middle.next = reverse(middle.next);
ListNode p1 = head, p2 = middle.next;
while (p1 != null && p2 != null && p1.val == p2.val) {
p1 = p1.next;
p2 = p2.next;
}
return p2 == null;
}
private ListNode findMiddle(ListNode head) {
if (head == null) {
return null;
}
ListNode slow = head, fast = head.next;
while (fast != null && fast.next != null) {
slow = slow.next;
fast = fast.next.next;
}
return slow;
}
private ListNode reverse(ListNode head) {
ListNode prev = null;
while (head != null) {
ListNode temp = head.next;
head.next = prev;
prev = head;
head = temp;
}
return prev;
}
}```